The present invention relates to a printing apparatus such as a printer, and more particularly, to a technique for preventing heat generation from a drive section for a print head.
Since an ink jet printer can produce a high-resolution, full-color print, the ink jet printer is now in widespread use. Because of ease of control operation, such as finely-controlled formation of ink dots, a print head drive system for ejecting ink droplets by utilization of flexural vibration of a piezoelectric element has become pervasive as a print head drive system of such an ink jet printer. When a print head is driven by utilization of such flexural vibration of a piezoelectric element, the power consumed in a power transistor for activating a piezoelectric element is approximately 10 to 30 W. If a printing operation involving a high nozzle operating rate (i.e., a high duty factor) is performed continuously, the temperature of the power transistor increases. In the event that the temperature of the power transistor exceeds a temperature of 150xc2x0 C., the power transistor is subjected to thermal breakdown. In order to prevent occurrence of such a problem, a cooling fan or a heat sink for heat radiation purpose is provided in the vicinity of a drive section of the print head. Heat of the power transistor is cooled by activation of the cooling fan or dissipated through a heat sink, thereby preventing a rise in the temperature of the power transistor.
However, when, for example, a cooling fan is used, a drive circuit or control circuit of the fan must be incorporated in a printer. As a result, the printer per se becomes bulky, or an increase in the number of parts adds to cost.
However, in the case of an ink jet printer in which one head is constituted of a total of six nozzle groups; that is, a black (K) nozzle group, a yellow (Y) nozzle group, a cyan (C) nozzle group, a magenta (M) nozzle group, a light cyan (LC) nozzle group, and a light magenta (LM) nozzle group, switching semiconductor elements for driving ink nozzles are mounted for the respective nozzle groups. For instance, in the case of a printer equipped with a print head constituted of 48 nozzles (n=48) for each color, 48 switching circuits are included in a switching semiconductor element to be constituted into one chip. At the time of assembly of an ink jet printer, chips are attached to respective nozzle groups. When an attempt is made to drive the respective nozzle groups, a drive voltage is applied to a total of 288 piezoelectric vibrators. A case where all nozzles for one color have ejected ink is taken as a nozzle operating rate of 100%. In a case where a total of 288 nozzles for six ink colors are caused to eject ink, a nozzle operating rate of 600% is achieved.
However, when a normal printing operation is performed through use of a color ink jet printer, a case where ink is ejected simultaneously from all nozzles of all color heads; that is, a case where a nozzle operating rate of 600% is achieved, would be extremely unusual. For example, even at the time of printing of bit map data of true color commonly used as a print sample, the nozzle operating rate does not exceed 130%.
For this reason, it is considered that a transistor capable of withstanding a nozzle operating rate of about 200%, allowing for a safety factor of about 70%, is selected and adopted in a process for assembling a printer and that a heat sink of sufficient size for continuously operating at a nozzle operating rate of 200% is attached to the transistor for radiation purpose.
However, depending on the design of a printer driver of a host computer or the configuration of an operating system, there may arise a case where a nozzle operating rate exceeds 200%. However, if a transistor capable of withstanding excessive load such as a nozzle operating rate of 600% is selected, costs will increase. Moreover, use of a large heat sink results in upsizing of a component to be mounted.
For these reasons, the following technique is proposed in, e.g., Japanese Patent Publication No. 2000-238379A. Specifically, an initial temperature of a print head is determined on the basis of a detection signal output from a temperature sensor provided in a printer. Temperature rises in individual sections of the printer from the initial temperature are predicted on a per-predetermined-print-area basis. If the predicted temperature may exceed a predetermined threshold value, a print speed is regulated. Even when a printing operation is continuously performed at high duty factor, the thus-proposed technique enables prevention of thermal breakdown of a power transistor, as well as limiting a drop in throughput to a minimum level.
However, if a difference exists between the thus-predicted temperature and an actual temperature, there may arise a case where a print speed is limited more than necessary when a printing operation is performed at high duty factor, or where overheating of the power transistor cannot be prevented.
It is therefore an object of the present invention to provide a printing apparatus which effectively prevents heating of a drive section of a print head even at the time of printing operation being performed at high duty factor without involvement of a cost hike or upsizing of components to be mounted and suppression of a drop in print processing speed to a minimum.
In order to solve the problem, according to the present invention, there is provided a printing apparatus, comprising:
a print head mechanism, which performs printing predetermined image information on a fed recording medium, based on a given control signal;
a detector, which detects an operating rate of the print head mechanism at a predetermined region on the recording medium every time when printing with respect to the predetermined region is finished;
a comparator, which compares the operating rate with a given threshold operating rate; and
controller, which halts the print head mechanism, when the operating rate exceeds the threshold operating rate, for a halting time period corresponding to an excess amount of the operating rate.
In this configuration, there can be provided a highly-reliable printing apparatus which can suppress a drop in print processing speed to a minimum value even at the time of a printing operation to be performed at high duty factor and thereby inhibit heating of a driving section of the print head mechanism.
The printing apparatus may be a serial printer, the recording medium may be print paper, and the predetermined region may be either one raster or one page defined on the recording medium.
The operating rate is an average operating rate which is determined by either an ink dot count or a consumed ink amount while the print head mechanism performs printing the image information on the recording medium.
The threshold operating rate is varied in accordance with change in an external ambient temperature of the printing apparatus. The change in the external ambient temperature is detected based on a temperature detection signal sent from a temperature detector provided externally.
The operating rate may be varied in accordance with change in an internal ambient temperature of the printing apparatus. The change in the internal ambient temperature is detected based on a temperature detection signal sent from a temperature detector provided with the print head mechanism.
The operating rate may be varied in accordance with change in a temperature of a semiconductor switching element in a drive circuit for driving the print head mechanism. The change in the internal ambient temperature is detected based on a temperature detection signal sent from a temperature detector provided with the semiconductor switching element.
When the halting time period is longer than either a raster changing time period of the print head mechanism or a standby time period for which printing on a new recording medium is started, the print head mechanism may be halted for a time period corresponding to a difference between the halting time period and the raster changing time period or the standby time period.
According to the present invention, there is also provided an apparatus for controlling a print head mechanism, which performs printing predetermined image information on a fed recording medium, based on a given control signal, comprising:
a detector, which detects an operating rate of the print head mechanism at a predetermined region on the recording medium every time when printing with respect to the predetermined region is finished;
a comparator, which compares the operating rate with a given threshold operating rate; and
controller, which halts the print head mechanism, when the operating rate exceeds the threshold operating rate, for a halting time period corresponding to an excess amount of the operating rate.
According to the present invention, there is also provided a method for controlling a print head mechanism, which performs printing predetermined image information on a fed recording medium, based on a given control signal, comprising the steps of:
detecting an operating rate of the print head mechanism at a predetermined region on the recording medium every time when printing with respect to the predetermined region is finished;
comparing the operating rate with a given threshold operating rate; and
halting the print head mechanism, when the operating rate exceeds the threshold operating rate, for a halting time period corresponding to an excess amount of the operating rate.
According to the present invention, there is also provided a computer program for controlling a print head mechanism, which performs printing predetermined image information on a fed recording medium, based on a given control signal, comprising the steps of:
detecting an operating rate of the print head mechanism at a predetermined region on the recording medium every time when printing with respect to the predetermined region is finished;
comparing the operating rate with a given threshold operating rate; and
halting the print head mechanism, when the operating rate exceeds the threshold operating rate, for a halting time period corresponding to an excess amount of the operating rate.
According to the present invention, there is also provided a printing apparatus, comprising:
a temperature monitor, which monitors a temperature of a transistor which generates a voltage waveform for driving a print head to transmit temperature information; and
a drive controller, which drives the print head while reducing an operation rate of nozzles in the print head, based on the temperature information transmitted from the temperature monitor.
The drive controller may include a storage which stores temperatures of the transistor to be monitored in association with numbers of operable nozzle. The drive controller may read a number of operable nozzle from the storage based on the temperature information so that only the read number of nozzles are operated to reduce the operating rate.
The numbers of operable nozzle may be stored in association with each color nozzle array.
The numbers of operable nozzle for the respective nozzle arrays may be identical with each other, or may be different from each other.
The number of operable nozzle may be determined with respect to total number of nozzles of all nozzle arrays. The drive controller may set the number of operable nozzle for each color nozzle array in a real-time manner.
The drive controller may include a past operation evaluator, which determines whether the reduction of nozzle operation rate is performed upon a current printing, based on a past nozzle operation of the print head.
The past operation evaluator may perform the determination based on a time period elapsed from a previous driving of the print head.
The past operation evaluator may perform the determination based on an accumulated count of nozzle operation at a previous driving of the print head.
The drive controller may perform the reduction of nozzle operation rate, only when a print head is not in a scanning operation.
According to the present invention, there is also provided a printing apparatus, comprising:
a temperature monitor, which monitors a temperature of a transistor which generates a voltage waveform for driving a print head to transmit temperature information; and
a drive controller, which drives the print head while reducing an operation rate of nozzles in the print head, based on the temperature information transmitted from the temperature monitor, wherein:
the drive controller includes a storage which stores temperatures of the transistor to be monitored in association with time periods for which nozzle operation is halted; and
the drive controller reads a time period from the storage based on the temperature information so that nozzle operation is halted for the read time period.
According to the present invention, there is also provided a printing apparatus, comprising:
a temperature monitor, which monitors a temperature of a transistor which generates a voltage waveform for driving a print head to transmit temperature information;
a drive controllers which drives the print head while reducing an operation rate of nozzles in the print head, based on the temperature information transmitted from the temperature monitor; and
a storage which stores temperatures of the transistor to be monitored in association with time periods for which nozzle operation is halted,
wherein the drive controller reads a time period from the storage based on the temperature information so that nozzle operation is halted for the read time period.
In the above configurations, the temperature of a transistor is monitored, and temperature information is handed to the drive controller. The print head can be actuated by reducing the operating rate of nozzles of the print head with utilization of the temperature information. Further, there can be achieved fine head drive control in which, even when operation of the head is halted by utilization of the temperature information, printing operation is not halted as a fatal error, and in which a most appropriately-conceivable halted time period can be selected from alternatives. As a result, mounted components can be protected from a risk of heating, thus increasing the degree of freedom in selecting and designing components.